Pickling solution for metals



Patented June 25, 1946 momma SOLUTION FOR METALS Elmer K. Bolton, Wilmington, Del., assignmto E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application January 29, 1943, Serial No. 473,977

11 Claims. 1

This invention relates to a process for inhibiting the corrosion of metals caused by contact with acidic solutions.

It is well known that strongly acidic solutions are highly corrosive to most metals. Nevertheless, many important industrial operations require the contact of metals with strongly acidic solutions. For example, in the process of fabricating many articles o iron, steel and also nonferrous metals and alloys, it is often necessary to treat the metal with an aqueous solution of a strong acid in order to remove the layer of oxide or scale formed during previous treatments. This operation, which is conducted on a large scale, is known as metal pickling. Other industrial operations involving the contact of metals with strongly acidic solutions include the acid treatment of petroleum, regeneration of cellulose, and the storage and transportation of acidic solutions.

The corrosion of metals which results from their contact with strongly acidic solutions in the above-mentioned operations as well as many others results in a considerable loss of metal and acid and also the frequent need for replacement of metal equipment. It has been known for some time that the amount of corrosion can be reduced by employing in the acidic solution, relatively small amounts of certain materials that have been called pickling inhibitors or corrosion inhibitors. While the principal requirement of a corrosion inhibitor is that it prevents the attack on the metal by the acid, there are several other properties which are essential to a good inhibitor, and these vary widely depending upon the particular application involved. Some of these other important properties are freedom from objectionable odor, ease of addition to the acidic solution, and stability. In addition, and especially in such operations as the pickling of metals prior to galvanizing or metal plating in acid, it i important that the corrosion inhibitor employed leaves the metal surface with the proper film characteristics. Moreover, in pickling operations the addition of corrosion inhibitors should not decrease markedly the rate at which the undesirable scale and metal oxide is removed by the acidic solution. One of the chief drawbacks to many corrosive inhibitors is their low solubility in water or aqueous acidic solutions. This considerably complicates their use since such materials must be handled uusally as colloidal solutions, emulsions or as solutions in concentrated sulfuric acid. Moreover the water-insoluble materials tend to separate from the baths as sludge and are more difficult to rinse from the treated metal.

.An object of the present invention, therefore, is to prevent the corrosion of metals by acidic solutions. Another object is the prevention of corrosion of metals by acidic solutions by means of an efficient inhibitor that is freely water-soluble. Another object is to provide a metal cleaning solution which is relatively non-corrosive to the metal itself. Other objects will be apparent from the following description of the invention.

These objects are accomplished by employing in an aqueous acidic solution which is in contact with a metal the corrosion of which is to be inhibited, a substance selected from the class comprising an aliphatic polyhydroxythiol. particularly a polyhydroxythiol containin carbon at oms an aving a configuration corresponding to that of a monose sugar, and the-disulfldes of such aliphatic polyhydroxythiols.

In practicing this invention a fraction of a per cent of an aliphatic polyhydroxythiol, which may be obtained readily by the process described in the copending application of W. A. Lazier and F. K. Signaigo, Serial No. 357,417, filed Septem-- ber 19, 1940, or the corresponding dlsulfide which is obtainable from the thiol by oxidation with mild oxidizing agents such as a halogen, air or hydrogen peroxide, is dissolved in the acidic aqueou solution which is to be in contact with the metal whose corrosion is to be minimized. It is usually convenient to dissolve the polyhydroxythiol in water to a fairly high concentration and to employ this solution for adding the thiol to the aqueous acid. The following examples show in greater detail the practice of this invention. The mounts of materials referred to are in terms of weight unless otherwise specified.

EXAMPLE I The strong inhibiting action of a polyhydroxythiol on the corrosion of steel by strongly acidic solutions is shown by the following experiments.

Samples of black steel sheet cut from a commonstrip were descaled, pickled, degreased, washed.

(CH2OH(CHOH) 4CH2SH) prepared as described in the aforementioned application by hydrogenating a mixture of dextrose and sulfur over a sulfactive catalyst. The acidic solutions were then heated at 70 C. and the test strips were immersed in the solutions for 20 minutes, then removed from the tubes, washed with water, dried, and reweighed. The results are listed in Table I.

Tssu: I

Eflect ol I-thiosorbitol on the rate of attack of various acids on low carbon steel strip at 70 C.

Per cent of l-thiosorbitol in acidic solution- 0.00 0.05 0.10 0.20 0.50 1.00 2.50 Weight loss of metal (g./sq. dm.)- 1.41 0.24 0.13 0.099 0.061 0.024 0.029 6% RC1:

Per cent of l-thiosorbitol in acidic solution 0.00 0.01 0.05 0.10 0.20 Weight loss of metal (g./sq. dm.) 0.60 0.081 0.057 0.047 0.039 10% EC Per cent of l-thiosorbitol in acidic solution 0.00 0.05 0.10 0.50 Weight loss of metal (g./sq. dm.) 1.31 0.35 0.27 0.20

These data show the inhibiting action of 1- thiosorbitol. For example, under the conditions of test 10% sulfuric acid solution caused a weight loss of 1.41 g./sq. dm. whereas with the same solution but containing 0.05% of l-thiosorbitol the weight loss was reduced to about one-sixth of this value. The addition of 0.10% of thiosorbitol reduced the weight loss to onetenth and the addition of 1% decreased the weight loss to approximately one-sixtieth of the value observed in the absence of the inhibitor. It is to be noted that the inhibiting action of 1- thiosorbitol is even more pronounced in the case of aqueous hydrochloric acid solution. The corrosion of aqueous hydrochloric acid solution is likewise effectively inhibited by the addition of very small amounts of the polyhydroxythiol.

EXAMPLE II Polhydroxythiols are likewise effective in preventing the corrosion on stainless steel alloys, as is shown by the following experiment. Samples of stainless steel strip were degreased, dried, weighed and immersed for 20 minutes at 70 C. in an aqueous solution containing 10% of hydrochloric acid and a similar solution containing in addition 0.04% of l-thiosorbitol. The samples were then removed from the solution, washed, dried, and reweighed. The strip immersed in the solution containing no thiosorbitol lost 0.71 g./sq. dm. of metal during the test whereas the strip immersed in the acid solution containing 0.04% of l-thiosorbitol but otherwise under similar conditions lost but 0.11 g./sq. dm. of metal, corresponding to approximately onesixth as much corrosion.

EXAMIPL'EIII The use of a polyhydroxythiol to prevent corrosion during the pickling of iron is shown as follows. Samples of sheet steel containing black scale were degreased in acetone, dried, and

4 weighed. These samples were then subjected to the action of an aqueous solution containing 10% of sulfuric acid and varying amounts of l-thiosorbitol at 70 C. for two periods of one hour each. The amount of corrosion resultin expressed in weight loss, is shown in the following Table II.

Tact: II

Corrosion of sheet steel during pickling operation Sample 1 Sample 2 Sample 3 Percent of thiosorbitol added 0. 30 l. 0 0. 0 Weight loss first hour, g./sq. dm. 0. 80 0. 63 .i. 8 Weight loss second hour, g.lsq. dm. 0. 29 0.092 3. 5

EXAMPLEIV A nickel base alloy, Hastelloy C., is subjected to the action of an acidic cellulose regenerating bath such as is used in manufacturing viscose rayon. The test is run in duplicate at 63 0., one bath containing in addition to th regular components, 0.10% of thiosorbitol and the other bath containing no thiosorbitol. The amount of corrosion of th nickel alloy at the end of the test by the bath containing thiosorbitol was only three-sevenths of the amount of corrosion caused by the bath containing no thiosorbitol.

In the foregoing examples we have illustrated the use of l-thiosorbitol, a polyhydroxythiol, for inhibitin the corrosive attack of acidic solutions on metals. This invention is, however, not limited to the particular materials and conditions used for illustration. Instead of l-thiosorbitol we may use with similar advantageous results in the process of this invention, other polyhydroxythiols preferably containin at least four carbon atoms and having a structure identical in number of carbon atoms, number of hydroxyl groups, and configuration with a member of the group of compounds hiown as aldose sugars and ketose sugars. For example, 2-thiosorbitol, l-thiomannitol, and other polyhydroxythiols obtainable by the hydrogenation of an aldose or ketose sugar in the presence of hydrogen sulfide as described in the abovementioned copending application, Serial No. 357,- 417, may be employed in the process of this invention. It is preferred to employ the polyhydroxythiols and especially l-thiosorbitol, but the corresponding disulfides derivable from these by mild oxidation may also be used to advantage in this invention.

The amount of polyhydroxythiol or its disulfide to be employed will vary depending upon the particular metal, acidic solution, degree of corrosion resistance required, or other considerations and is readily determined by trial. Usually an amount of thiol of the order of 0.001 to about 1% by weight of the acidic solution is suflicient to inhibit the corrosion to a considerable degree. As has been illustrated in the foregoing examples, the polyhydroxythiols are efiective corrosion inhibitors for a variety of acids. The process of this invention is not only applicable to systems involving mineral acids such as sulfuric, hydrochloric, phosphoric acids and the like, but also or anic acids as for example, acetic, chloroacetic, and propionic acids.

The polyhydroxythiols are effective corrosion inhibitors at room temperature but since these compounds are quite stable toward hot acidic solutions they may be used effectively at elevated temperatures.

The examples have illustrated the corrosion inhibiting effect of polyhydroxythiols in the case of certain ferrous and non-ferrous alloys, but the invention is applicable to metals in general including iron, ferrous alloys, nickel, nickel base alloys, copper and copper base alloys such as brass, bronze, etc.; lead and lead alloys, and the like.

This invention comprises an improved process for repressing the corrosive attack of acidic solutions on metals, thereby increasing the emciency of many commercial processes involving th contact of metals with strongly acidic solutions such as in pickling or cleaning of iron, steel, and nonferrous metals; the regeneration of cellulose, the refining of petroleum, and the storage and transportation of acidic solutions.

As many apparently widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments shown and described.

I claim:

1. A highly ionized mineral pickle acid solution having incorporated therein from about 0.01% to about 2.5% by weight oi the acid solution of an aliphatic polyhydroxythiol containing at least 4 carbon atoms and having a configuration corresponding to that of a monose sugar.

2. A pickling solution for ferrous metals comprising an aqueous solution of sulfuric acid having incorporated therein from about 0.01% to about 2.5% ,by weight of the acid solution of an aliphatic polyhydroxythio] containing at least 4 carbon atoms and having a configuration corresponding to that of a monose sugar.

3. A pickling solution for ferrous metals com- Certificate of Correction Patent No. 2,402,596.

4. A pickling solution for ferrous metals comprising an aqueous solution of sulfuric acid having incorporated therein from about 0.01% to about 2.5% by weight of the acid solution of l-tbiosorbitol.

5. A pickling solution for ferrous metals comprising an aqueous solution of hydrochloric acid having incorporated therein from about 0.01% to about 2.5% of l-thiosorbitol.

6. The process for repressing the corrosive attack of acidic solutions on metals which comprises adding to said solutions from about 0.01% to about 2.5% by weight of the acid solution of an aliphatic polyhydroxythiol containing at least 4 carbon atoms and having a configuration corresponding to that of a monose sugar.

7. The process for repressing the corrosive attack of acidic solutions on metals containing iron which comprises adding to said solutions from about 0.01% to about 2.5% by weight of the acid solution oi l-thiosorbitol.

8. The process for repressing the corrosive attack of aqueous solutions of sulfuric acid on metals containing iron which comprises adding to said solutions from about 0.01% to about 2.5% by weight of the acid solution of an aliphatic polyhydroxythiol containing at least 4 carbon atoms and having a configuration corresponding to that of a monose sugar.

9. The process for repressing the corrosive attack of aqueous solutions of sulfuric acid on metals containing iron which comprises adding to said solutions from about 0.01% to about 2.5% by weight of the acid solution of l-thiosorbitol.

10. The process for repressing the corrosive attack of aqueous solutions of hydrochloric acid on metals containing iron which comprises adding to said solutions from about 0.01% to about 2.5% by weight of the acid solution of an aliphatic polyhydroxythiol containing at least 4 carbon atoms and having a configuration corresponding to that of a monose sugar.

11. The process for repressing the corrosive attack of aqueous solutions of hydrochloric acid on metals containin irnn mhinh Mama-i- June 25, 1946.

ELMER K. BOLTON It is hereby certified that err numbered patent requiring correc read corrosion; column 2, line 2, for

v f lolh dro thiols read amounts, il i dl 5 bf t i r 5% insert lg wel g ltt of the acuitc SOZlLtLOIt; and that Patent should be read with these corrections therein that the same column 6, line 9, 01 the said Letters a ear in the printed specification of the above thin 21 s follows: Column 1, line 49, for corrosive:

uusally read usually; line 42, for mounts read Polyhydroxyth'iols;

' Office. ma conform to the record of the case 1n the Patent Signed and sealed this 3rd day of September, A. D. 1946.

LESLIE FRAZER, 

